Tire/wheel assembly and run-flat support member

ABSTRACT

A tire/wheel assembly comprising: a wheel having a disc and a rim provided on the outer peripheral edge of the disc in such a manner that the widthwise center of the rim is offset towards one side; a pneumatic tire mounted on the rim; and a run-flat support member disposed in the cavity of the pneumatic tire, the run-flat support member having an annular shell and elastic rings, the annular shell including a support surface located radially outwardly thereof and two leg portions formed radially inwardly thereof in a straddling state, the support surface having a plurality of convexly curved surface sections that are widthwisely arranged, the elastic rings supporting the leg portions on the rim. One of the elastic rings located on the opposite side of the rim to the offset side is smaller in rigidity than the other of the elastic rings located on the offset side.

TECHNICAL FIELD

The present invention relates to tire/wheel assemblies and run-flatsupport members, and more particularly, to a tire/wheel assembly and arun-flat support member used therefor, in which durability can beimproved.

TECHNICAL BACKGROUND

In response to demands in the market, there have been proposed manytechnologies which allow a vehicle to urgently travel several hundredskilometers when a pneumatic tire thereof is punctured during traveling.These many proposals include a technology that allows for run-flatoperation by supporting a punctured pneumatic tire with a support membermounted on a rim in the cavity of the tire seated on the rim.

The above run-flat support member comprises an annular shell having asupport surface located radially outward with two convexly curvedsurface sections arranged widthwisely thereof and a leg structure in anopen state disposed radially inward, and elastic rings attached to twoleg portions of the leg structure, and is supported on the rim via theelastic rings. The run-flat support member allows existing wheels to beused without any specific modifications, and can therefore beadvantageously adopted without causing confusions in the market (seeJapanese Patent Application Publication Nos. 10-297226 and 2001-519279,for example).

Wheels in common use comprise a disc and a rim fixed to the outerperipheral edge of the disc in such a manner that the widthwise centerof the rim is off set towards one side (vehicle inner side), therebyincreasing the space of the vehicle inner side surrounded by the discand rim to accommodate parts mounted on the vehicle.

A tire/wheel assembly including the above run-flat support membermounted on a wheel with such an offset rim has such a problem that aportion of the tire supported by one convexly curved surface sectionlocated on the opposite side (vehicle outer side) of the rim to theoffset side is more subject to destruction than a portion of the tiresupported by the other convexly curved surface section located on theoffset side (vehicle inner side) during run-flat operation, which is oneof the causes that degrade durability in run-flat mode.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a tire/wheel assemblyand a run-flat support member capable of improving run-flat durability.

In order to achieve the above object, a tire/wheel assembly according tothe present invention comprises: a wheel having a disc and a rimprovided on an outer peripheral edge of the disc in such a manner that awidthwise center of the rim is offset towards one side; a pneumatic tiremounted on the rim, the pneumatic tire having a cavity; and a run-flatsupport member disposed in the cavity of the pneumatic tire, therun-flat support member having an annular shell and elastic rings, theannular shell comprising a support surface located radially outwardlythereof and two leg portions formed radially inwardly thereof in astraddling state, the support surface having a plurality of convexlycurved surface sections that are widthwisely arranged, the elastic ringssupporting the leg portions on the rim, wherein one of the elastic ringslocated on an opposite side of the rim to the offset side is smaller inrigidity than the other of the elastic rings located on the offset side.

A run-flat support member according to the present invention to bemounted on a wheel having a disc and a rim provided on an outerperipheral edge of the disc in such a manner that a widthwise center ofthe rim is offset towards one side, comprises: an annular shell having asupport surface located radially outwardly thereof and two leg portionsformed radially inwardly thereof in a straddling state, the supportsurface having a plurality of convexly curved surface sections that arewidthwisely arranged; and elastic rings for supporting the leg portionson the rim, wherein one of the elastic rings located on an opposite sideof the rim to the offset side is smaller in rigidity than the other ofthe elastic rings located on the offset side.

According to the present invention described above, since the elasticring located on the opposite side is more flexible than the elastic ringlocated on the offset side, the elastic ring on the opposite sidecounterbalances the offset side of the rim in flexure during run-flatoperation, resulting in that the difference between the contact pressureof the convexly curved surface section located on the opposite sideagainst the inner surface of the pneumatic tire and the contact pressureof the convexly curved surface section located on the offset sideagainst the inner surface of the pneumatic tire can be smaller thanbefore. Therefore, the inner surface of the pneumatic tire can besupported by the convexly curved surface sections with balance betterthan before, so the destruction of the tire portion supported by theconvexly curved surface section located on the opposite side can besuppressed, enhancing run-flat durability.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a partial cross-sectional view showing an embodiment of atire/wheel assembly according to the present invention operated in arun-flat condition.

BEST MODES FOR CARRYING OUT THE INVENTION

According to the present invention, the run-flat support member isformed as an annular member to be inserted into the cavity of apneumatic tire. This run-flat member is formed so as to have an outerdiameter smaller than the diameter of the cavity of the pneumatic tireto maintain a constant distance from the inner surface of the tirefacing the cavity, and is formed so as to have an inner diameter whichis substantially equal in size to the inner diameter of the beads of thepneumatic tire. The run-flat support member is inserted into thepneumatic tire, and mounted on the rim of a wheel together with thepneumatic tire to form a tire/wheel assembly. This tire/wheel assemblyis mounted on a vehicle, and when the pneumatic tire is punctured duringtraveling, the punctured tire is supported by the radially outer surfaceof the run-flat support member to thereby allow for run-flat operation.

The above-described run-flat support member includes a annular shell andelastic rings as main parts.

The annular shell has a continuous support surface formed radiallyoutward for supporting a punctured tire, and right and left sidewalls astwo leg portions in a straddling shape disposed radially inward. Theradially outer support surface is convexly formed radially outward inacross-sectional shape taken along a plane orthogonal to thecircumferential direction thereof, and includes at least two convexlycurved surface sections that are widthwisely arranged. Formation of thesupport surface in such a way as to arrange two or more convexly curvedsurface sections provides the support surface with two or more dispersedcontact areas with respect to the inner surface of the tire (innersurface facing the cavity) to thereby reduce localized wear on the tireinner surface, and therefore, the run-flat operation distance can beextended.

The elastic rings are attached to the ends of the two leg portionsformed in a straddling state on the radially inner side of the annularshell, respectively, and come into engagement with the right and leftseats of the rim to thereby support the annular shell. The elastic ringsare formed of rubber or elastic resin, and not only mitigate thevibration and impact of the annular shell receiving from the puncturedtire, but also prevent slipping with respect to the rim seats to stablysupport the annular shell.

The annular shell is formed of a rigid material since the run-flatsupport member has to support a vehicle weight through the puncturedtire. Constituent materials used for the rigid material include metals,resins and the like. The metals may include, for example, steel andaluminum. The resins may include thermoplastic resins and thermosettingresins. The thermoplastic resins may include nylon, polyester and thelike, and the thermosetting resins may include epoxy resins, unsaturatedpolyester resins, etc. The resins may be used alone or mixed withreinforcing fibers as fiber-reinforced resins.

The elastic rings may be formed of any kind of rubber or elastic resinif they can stably support the annular shell. Examples of the rubber mayinclude natural rubber, isoprene rubber, styrene-butadiene rubber,butadiene rubber and butyl rubber, and examples of the elastic resin mayinclude resin foam such as polyurethane foam.

The run-flat support member used for a tire/wheel assembly according tothe present invention is premised on the structure described above.

An embodiment of the present invention will be described in detail belowwith reference to the attached drawing.

FIG. 1 is a cross-sectional view showing a main part of a tire/wheelassembly according to an embodiment of the present invention; referencenumeral 1 denotes a wheel, reference numeral 2 denotes a pneumatic tire,and reference numeral 3 denotes a run-flat support member.

The wheel 1 comprises a disc 1B and an annular rim 1A fixed to the outerperipheral edge of the disc 1B in such a manner that the widthwisecenter O of the rim is offset towards one side. The pneumatic tire 2 ismounted on the rim 1A and the run-flat support member 3 is disposed inthe cavity 2X of the pneumatic tire 2. The wheel 1, pneumatic tire 2,and run-flat support member 3 are arranged in coaxial alignment witheach other with respect to the axis (not shown) of rotation of the wheel1 so as to be in the form of an annulus.

Although not shown in the drawing, the pneumatic tire 2 has a carcassply extending between right and left beads 2B. A plurality of belt pliesare provided radially outwardly of the carcass ply in a tread 2A. A beadcore is embedded in each of the right and left beads 2B, and the carcassply has opposing ends that are turned up around the bead cores from theinner side towards the outer side of the tire.

The run-flat support member 3 comprises an annular shell 4 formed of arigid material such as metal or rein, and right and left elastic rings5A and 5B formed of an elastic material such as rubber or elastic resin.

The annular shell 4 includes a support surface 6 located radiallyoutwardly thereof with two convexly curved surface sections 6 a and 6 bthat are arranged widthwisely of the annular shell 4 and have thesubstantially same radius of curvature; the support surface 6 are spacedapart from the inner surface 2 a of the tread 2A of the pneumatic tire 2when the pneumatic tire 2 is operated in a normal condition, and whenpunctured, the support surface 6 supports the inner surface 2 a of thetread 2A of the punctured pneumatic tire 2.

The annular shell 4 also includes two side walls located radiallyinwardly thereof, formed as leg portions 7 a and 7 b that arestraddle-shaped, and the elastic rings 5A and 5B are attached to theradially inner sides of the leg portions 7 a and 7 b, respectively.

The right and left elastic rings 5A and 5B are different in rigidity,and the elastic ring 5A positioned on the opposite side of the rim tothe offset side is smaller in rigidity than the elastic ring 5Bpositioned on the offset side, according to the offset amount. Therigidity of the elastic ring 5A on the opposite side can be made lowerthan that of the elastic ring 5B on the offset side by, for example,making the elastic ring 5A higher in height than the elastic ring 5B onthe offset side (the width is equal) as shown in the drawing, making theelastic ring 5A thinner in thickness than the elastic ring 5B, using aelastic material for the elastic ring 5A having modulus of elasticitylower that that for the elastic ring 5B, or a combination thereof. It ispreferable, in terms of seating stability on the rim and ease ofdistinguishing the elastic ring 5A on the opposite side from the elasticring 5B on the offset side, that the rigidity of the elastic ring 5A bemade lower by making the elastic ring 5A on the opposite side higher inheight than the elastic ring 5B on the offset side.

The run-flat support member 3 having the elastic rings 5A and 5Bconstructed as described above is inserted into the cavity 2X of thepneumatic tire 2, and the elastic rings 5A and 5B of the run-flatsupport member 3 are seated on the rim seats 1 s, 1 s of the rim 1Atogether with the beads 2B, 2B of the pneumatic tire 2.

The present inventor has found the following through an intense study onthe cause of earlier destruction of a portion of the tire supported bythe convexly curved surface section 6 a located on the opposite side(vehicle outer side) of the rim to the offset side.

That is, the two convexly curved surface sections 6 a and 6 b supportthe inner surface 2 a of the tread 2A of the pneumatic tire 2 duringrun-flat operation as shown in FIG. 1; a tire support load then acts onthe rim 1A, causing greater deflections on the offset side of the rim1A. As a result, the contact pressure of the convexly curved surfacesection 6 a on the opposite side against the inner surface 2 a of thepneumatic tire 2 is higher than that of the convexly curved surfacesection 6 b on the offset side against the inner surface 2 a of thepneumatic tire 2, whereby a portion of the tire supported by theconvexly curved surface section 6 a on the opposite side is subject todestruction in advance of a portion of the tire supported by theconvexly curved surface section 6 b on the offset side.

Therefore, in the present invention, the elastic ring 5A located on theopposite side is smaller in rigidity than the elastic ring 5B located onthe offset side, as described above. This makes the elastic ring 5Apositioned on the opposite side more flexible than the elastic ring 5Bpositioned on the offset side, so the elastic ring 5A on the oppositeside counter balances the offset side of the rim 1A in flexure, whichcan make the difference between the contact pressure of the convexlycurved surface section 6 a located on the opposite side against theinner surface 2 a of the pneumatic tire 2 and the contact pressure ofthe convexly curved surface section 6 b located on the offset sideagainst the inner surface 2 a of the pneumatic tire 2 smaller thanbefore during run-flat operation. Therefore, since the inner surface 2 aof the pneumatic tire 2 can be supported by the convexly curved surfacesections 6 a and 6 b with balance better than before, the destruction ofthe tire portion supported by the convexly curved surface section 6 acan be suppressed, enhancing run-flat durability.

In the present invention, if G1 (/mm) is the rigidity of the elasticring 5A on the opposite side, and G2 (/mm) is the rigidity of theelastic ring 5B on the offset side, the relationship between therigidities G1 and G2 and the offset amount L (mm) of the rim 1Apreferably satisfies the following expression.0.0012≦(G2−G1)/(G1×L)≦0.020   (1)

The rigidity referred here is measured as follows.

First, the annular shell is removed from the elastic ring, and theelastic ring is then cut to obtain a sample having a length of 10 cm inthe circumferential direction of the ring. If the radially inner end ofthe leg portion of the annular shell is buried in the elastic ring, theannular shell is removed from the elastic ring in such a manner that theleg portion is cut off along the radially outer surface of the elasticring with the buried radially inner end of the leg portion being left inthe elastic ring. A load W (50 kgf (454 N)) is applied to the cut samplefrom a direction corresponding to the ring radial direction. That is,the sample is put on a horizontally flat test surface, keeping its ringradially inner surface side down, and a weight having a load of 50 kgf(454 N) is then put on the sample to compress it with the weightcontacting the entire upper surface of the sample. The amount δ ofdeflection that is defined as the amount of compression at this time ismeasured at a room temperature, and the reciprocal of the measurementvalue is a value (/mm) of the rigidity of the elastic ring.

The offset amount L is a wheel offset distance defined in normal wheels,which is a distance measured parallel to the tire axis (not shown) fromthe vehicle attachment face 1B1 of the center portion of the disc 1B tothe rim-widthwise center o of the rim 1A.

The satisfaction of the above expression (1) makes the differencebetween the contact pressures of the convexly curved surface portions 6a and 6 b against the inner surface 2 a of the pneumatic tire 2 smaller,whereby the convexly curved surface portions 6 a and 6 b can come intocontact therewith more evenly; therefore, the inner surface 2 a of thepneumatic tire 2 can be supported by the convexly curved surfacesections 6 a and 6 b with much better balance; accordingly, run-flatdurability can be further improved. More preferably, the above range isfrom 0.0020 to 0.015.

When the height of the elastic rings 5A and 5B is changed to vary therigidity, the elastic ring 5A on the opposite side is preferably 3 mm to14 mm, and more preferably 5 mm to 10 mm higher than the elastic ring 5Bon the offset side in terms of rendering the contact pressures of theconvexly curved surface portions 6 a and 6 b more even. It should benoted that the other things other than the height of the elastic rings5A and 5B, that is, the material and width of the elastic rings 5A and5B are the same.

The specification by the expression described above is preferablyadopted in the case of running straight in the run-flat mode; in thecase of run-flat operation including turning operation in which lateralforces are applied, if M is a ratio M2/M1 where M1 is the wheel-radialdeflection amount at a position of the radially most inwardly locatedouter edge 1 x of the rim flange 1 e on the opposite side of the rim 1Ato the offset side and M2 is the wheel-radial deflection amount at aposition of the radially most inwardly located outer edge 1 y of the rimflange 1 f on the offset side of the rim 1A, the relationship betweenthe rigidity G1 (/mm) of the elastic ring 5A on the opposite side andthe rigidity G2 (/mm) of the elastic ring 5B on the offset sidedescribed above preferably satisfies the following expression inrelation to the ratio M.0.009≦(G2−G1)/(G1×M)≦0.125   (2)

The deflection amount M1, M2 referred here is a deflection amountmeasured when the pneumatic tire is mounted on a standard rim describedin JATMA (JATMA YEAR BOOK 2002), an air pressure of 200 kPa is appliedthereto, and a load of 80% of the load ability corresponding to an airpressure of 200 kPa described in the JATMA is applied thereto in theradial direction and lateral direction (toward the offset side) of thetire.

The deflection amount M1 of the opposite side of the rim 1A isrepresented by “+” when deflected radially outwardly of the wheel, andby “−” when deflected radially inwardly of the wheel. The deflectionamount M2 of the offset side of the rim 1A is represented by “+” whendeflected radially inwardly of the wheel, and by “−” when deflectedradially outwardly of the wheel. The reason why specified as describedabove is that, when vertical load and lateral force are applied to thetire/wheel assembly during turning operation, a moment of force iscreated counterclockwise around the center of the tire in the tire/wheelassembly shown in FIG. 1, whereby the opposite side of the rim 1Adeflects radially outward and the offset side of the rim 1A deflectsradially inward.

If it is not easy to decide the positions of the radially most inwardlylocated outer edges 1 x and 1 y because the regions including the outeredges 1 x and 1 y are chamfered in the form of circular arcs or the likefor purposes of rim design, the central positions of the chamfered facesin a cross-sectional shape can be the positions of the outer edges 1 xand 1 y. Since M in the above expression is obtained by relativecomparison of the deflection amounts M1 and M2, there is no problem withthe positions of the outer edges 1 x and 1 y decided as mentioned above.

During turning operation of a vehicle, a great lateral force toward theouter side of the vehicle is applied to a tire located outwardly of theturning vehicle, that is, a tire mounted on the left side of the vehiclewhen turning right, and a tire mounted on the right side of the vehiclewhen turning left. A wheel 1 offset as described above is mounted on avehicle with its offset side facing to the vehicle; therefore, thesatisfaction of the above expression (2) can make the difference betweenthe contact pressures of the convexly curved surface sections 6 a and 6b against the inner surface 2 a of the pneumatic tire 2 further smallerduring run-flat turning operation with the lateral force appliedthereto, thereby putting the convexly curved surface sections 6 a and 6b into contact therewith more evenly. Therefore, the run-flat supportmember 3 can support the inner surface 2 a of the pneumatic tire 2 viathe convexly curved surface sections 6 a and 6 b of the annular shell 4with much better balance, thus further improving run-flat durability.The above range is preferably 0.014 to 0.100.

In the above embodiment, an example is shown of the case where thesupport surface 6 of the annular shell 4 has two convexly curved surfacesections 6 a and 6 b; however, the number of the convexly curved surfacesections is not limited to two, but may be a plural number that is threeor more.

The present invention is preferably applicable to a tire/wheel assemblyand a run-flat support member used for passenger cars in particular.

EXAMPLE 1

Prepared were tire/wheel assemblies according to the present invention(present example A, B and C) and prior art (conventional example), eachhaving a tire of size 205/55R16 and a rim of size 15×6 1/2JJ, thepresent invention tire/wheel assemblies each having a construction shownin FIG. 1 in which the elastic ring on the opposite side was smaller inrigidity than the elastic ring on the offset side, the prior arttire/wheel assembly being constructed such that the two elastic ringswere the same in rigidity.

In the present invention tire/wheel assemblies, the values of theexpression (G2−G1)/(G1×L) were as shown in Table 1.

Evaluation testing for run-flat durability was carried out on the testtire/wheel assemblies according to the following measurement method,obtaining the results shown in Table 1.

Run-Flat Durability

Each of the test tire/wheel assemblies having an air pressure of 0 kPawas mounted as a front right wheel on a front drive vehicle of 2.5 literdisplacement, and when the vehicle was run counterclockwise at a speedof 90 km/h in a circuit track, the distance until the vehicle could nolonger run was measured. The results of evaluation are represented by anindex number where the prior art tire/wheel assembly is 100. As thevalue is greater, run-flat durability is better.

The same sized tires and rims as described above were used for wheels ofthe vehicle other than the front right wheel, with the tires each havingan air pressure of 200 kPa.

TABLE 1 Conventional Present Present Present Example Example A Example BExample C (G2 − G1)/ — 0.0012 0.0040 0.020 (G1 × L) Run-flat 100 105 110106 Durability

From Table 1, it can be seen that the tire/wheel assemblies of thepresent invention can improve durability during run-flat operation.

EXAMPLE 2

Prepared were tire/wheel assemblies according to the present invention(present example D, E and F), each having the same sized tire and rim asin Example 1 and a construction shown in FIG. 1, in which the elasticring on the opposite side was smaller in rigidity than the elastic ringon the offset side, and the value of the expression (G2−G1)/(G1×M) wasas shown in Table 2.

Evaluation testing for run-flat durability was carried out on the testtire/wheel assemblies according to the measurement method shown inExample 1, obtaining the results shown in Table 2.

TABLE 2 Present Present Present Example D Example E Example F (G2 −G1)/(G1 × M) 0.009 0.025 0.125 Run-flat Durability 107 113 110

From Table 2, it can be seen that the tire/wheel assemblies of thepresent invention can improve durability during fun-flat operation.

INDUSTRIAL APPLICABILITY

The tire/wheel assembly of the present invention having theaforementioned excellent effect can be very effectively utilized as atire/wheel assembly that is mounted on a vehicle and allows for run-flatoperation.

1. A tire/wheel assembly comprising: a wheel having a disc and a rimprovided on an outer peripheral edge of the disc in such a manner that awidthwise center of the rim is offset towards one side and the rimundergoes greater deflections on its offset side than on its oppositeside during run-flat operation, a pneumatic tire mounted on the rim, thepneumatic tire having a cavity; and a run-flat support member disposedin the cavity of the pneumatic tire, the run-flat support member havingan annular shell and elastic rings, the annular shell comprising asupport surface located radially outwardly thereof and two leg portionsformed radially inwardly thereof in a straddling state, the supportsurface having a plurality of convexly curved surface sections that arewidthwisely arranged, the elastic rings supporting the leg portions onthe rim, wherein one of the elastic rings located on the opposite sideof the rim to the offset side is smaller in rigidity than the other ofthe elastic rings located on the offset side, wherein the plurality ofconvexly curved surface sections of the support surface of the annularshell are equal in radius of curvature, wherein further the elasticrings satisfy the following expression:0.0012≦(G2−G1)/(G1×L)≦0.020 where G1 is the rigidity of the elastic ringon the opposite side, G2 is the rigidity of the elastic ring on theoffset side, and L is the offset amount of the rim.
 2. A tire/wheelassembly comprising: a wheel having a disc and a rim provided on anouter peripheral edge of the disc in such a manner that a widthwisecenter of the rim is offset towards one side and the rim undergoesgreater deflections on its offset side than on its opposite side duringrun-flat operation, a pneumatic tire mounted on the rim, the pneumatictire having a cavity; and a run-flat support member disposed in thecavity of the pneumatic tire, the run-flat support member having anannular shell and elastic rings, the annular shell comprising a supportsurface located radially outwardly thereof and two leg portions formedradially inwardly thereof in a straddling state, the support surfacehaving a plurality of convexly curved surface sections that arewidthwisely arranged, the elastic rings supporting the leg portions onthe rim, wherein one of the elastic rings located on the opposite sideof the rim to the offset side is smaller in rigidity than the other ofthe elastic rings located on the offset side, wherein the plurality ofconvexly curved surface sections of the support surface of the annularshell are equal in radius of curvature, wherein further the elasticrings satisfy the following expression:0.009≦(G2−G1)/(G1×M)≦0.125 where G1 is the rigidity of the elastic ringon the opposite side, G2 is the rigidity of the elastic ring on theoffset side, and M is a ratio of M2/M1, M1 being a wheel-radial radialdeflection amount at a position of a radially most inwardly locatedouter edge of a rim flange on the opposite side of the rim, M2 being awheel-radial deflection amount at a position of a radially most inwardlylocated outer edge of a rim flange on the offset side of the rim.
 3. Atire/wheel assembly according to claim 1, wherein the elastic ring onthe opposite side is 3 mm to 14 mm greater in height than the elasticring on the offset side.
 4. A tire/wheel assembly according to claim 1or claim 2, wherein the elastic ring on the opposite side is smaller inrigidity than the elastic ring on the offset side corresponding to anoffset amount of the rim.